This invention relates to load handling apparatus and more particularly to coupling devices for engaging and subsequently releasing a load which is to be lifted or otherwise manipulated.
Coupling mechanisms for temporarily connecting load handling apparatus to an object which is to be moved should in many situations be lockable to avoid an accidental release of the load. When a heavy object is to be hoisted with a cable, the consequences of an inadvertent release of the suspended object are almost invariably extremely serious. This is also true of many operations where the object is to be pulled or pushed or manipulated through a combination of movements.
Avoidance of accidental disengagement of such coupling mechanisms may be necessary for reasons other than the weight of the object which is being handled or for reasons additional to the matter of weight. Considering one specific example, procedures for the underground storage of encased radioactive wastes, such as spent reactor fuel elements, may include the lowering of such materials into a vertical shaft by means of a cable. The fuel elements are then traveled horizontally along tunnels and lowered again into the underground storage chambers. The fuel elements must be recoverable after a period of years for reprocessing of the materials. A highly complex load manipulating system is required to accomplish these motions of the materials to be stored. The coupling mechanisms which temporarily engage the load during these operations must be reliably lockable to assure that the fuel element material cannot be accidentally released during handling. Moreover in this particular context engagement and disengagement including locking and unlocking of the coupling mechanism should be controllable from a remote location as in the absence of complicated protective procedures, operating personnel should not be required to be present in the vicinity of the materials.
An advantageous device for gripping a load to be moved is a ball and knob mechanism in which a hollow ball like element of the coupler has a key hole shaped opening. The larger part of the opening receives a knob which is secured to the load through a neck of narrower dimensions than the knob. The ball is then rotated to cause the neck to move into the slot and thereby engage the load for lifting or other movement. Prior coupling mechanisms of this general kind have in some cases been provided with locking means for blocking withdrawal of the knob through the large end of the opening except when the load is to be intentionally released. As heretofore designed such locking means complicate the process of engaging and disengaging the load by requiring separate manipulations of elements additional to those which accomplish the engaging and disengaging of the load. Further the prior locking systems are readily subject to operator error and are therefore not as reliable as would be desirable.
In one prior ball and knob coupler, for example, a pin must be manually inserted into the mechanism to block release of the knob from the ball and must later be manually removed to effect disengagement. Such a system is easily subject to operator mistake and is not compatible with load handling operations which are remotely controlled. As locking requires structural elements and operator actions additional to those which serve to engage the coupler with the load, a significant risk is present that the load may be lifted or manipulated with the coupling mechanism in an unlocked or in an imperfectly locked condition.